Photographic stabilizing baths inhibited against corrosion with polyalkylene glycols

ABSTRACT

STABILIZING BATHS WHICH ARE UTILIZED IN RAPID ACCESS PROCESSING OF PHOTOGRAPHIC ELEMENTS AND WHICH COMPRISE A THIOCYANATE STABILIZING AGENT AND AN ALUMINUM SALT WHICH FUNCTIONS AS A HARDENING AGENT FOR PHOTOGRAPHIC EMULSION ARE RENDERED LESS CORROSIVE TO PROCESSING EQUIPMENT BY INCORPORATION THEREIN OF A MINOR AMOUNT OF A POLYALKYLENE GLYCOL.

P. ZERNOV ETAL CARTON BLANK ALIGNING APPARATUS June 6, 1972 Fild Dec. 2, 1970 3 Sheets-Sheet l June 6, 1972 P. zERNov r- TAL 3,667,951

CARTON BLANK ALIGNING APPARATUS 3 Sheets-Sheet 2 Filed Dec. 2, 1970 32 j j; a

June 6, 1972 P. zERNov ErAL CARTON BLANK ALIGNING APPARATUS 3 Sheets-Sheet I5 Filed Dec. 2, 1970 l ffy:

United States Patent Olice 3,667,951 Patented June 6, 1972 3,667,951 PHOTOGRAPHIC STABILIZING BATHS INHIBITED AGAINST CORROSION WITH POLYALKYLENE GLYCOLS Henry J. Fassbender and Nelson S. Case, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y. No Drawing. Filed Mar. 3, 1969, Ser. No. 803,937

Int. Cl. G03c 5/38 U.S. Cl. 96-61 15 Claims ABSTRACT F THE DISCLOSURE This invention relates in general to photographic processing and in particular to rapid access processing. More specifically, this invention pertains to aqueous stabilizing baths used in rapid access processing which contain both a stabilizing agent and a hardening agent and to the incorporation of a polyalkylene glycol in such baths to reduce the corrosiveness thereof.

Rapid access processing, or, as it is sometimes called, stabilization processing, of photographic materials is well known and has been described in numerous patents, for example, U.S. Pats. 2,448,857 and 2,614,927. In such processing an imagewise exposed photographic element containing an incorporated developing agent is contacted with an activating bath to develop it and then with a stabilizing bath containing a compound which does not react with metallic silver and which forms a light-stable silver complex by reaction with undeveloped silver halide. Since this complex is transparent, or at least light in color, it is not necessary to wash it out of the element and, accordingly, both the fixing and washing steps utilized in conventional processing are eliminated with the result that substantial saving in processing time is achieved. The activating and stabilizing baths can be applied by dipping or spraying the element or by surface application with rollers or other mechanical devices and to facilitate completion of the process in the shortest possible time it is common practice to use automatic processors which effect the necessary contact with the processing solutions and then dry the element so as to render it immediately available for use.

The compounds which are most eiective as stabilizing or complexing agents are thiocyanates, in particular the ammonium and alkali metal thiocyanates, while the development step ordinarily involves the use of an alkaline development activator, for example, inorganic alkalis such as sodium or potassium hydroxide, alkali metal carbonates such as sodium or potassium carbonate, and organic agents such as quaternary ammonium bases. Thus, in the commercial utilization of rapid access processing, the exposed photographic element is contacted first with an activating bath which is strongly alkaline and then with a stabilizing bath which is an acidic solution containing the stabilizing agent along with other addenda. The apparatus used in carrying out the process is commonly referred to as a twobath stabilization processor.

Use of rapid access processing has been attended by certain difficulties and disadvantages which have hindered its commercial development. A major problem has been that the image has tended to lack stability, particularly under conditions of high temperature and/or high humidity, so that the process could not be successfully used with prints that had to be stored for long periods. A second critical problem is that the processed elements have tended to be tacky in nature as a result of the hygroscopic properties of the thiocyanate stabilizing agents and the action of the processing solutions in softening and swelling the emulsion layer, so that they cannot be easily handled or conveniently stored. These problems can be substantially overcome by careful control of the processing formulations and by the incorporation of various addenda therein. Thus, to aid in ensuring light stability of the image the thiocyanate stabilizing agent is ordinarily used in substantial excess of theoretical and to minimize the problem of tackiness there can be incorporated in the stabilizing bath an agent which functions to harden the emulsion layer, salts of aluminum being particularly effective compounds for this purpose. However, these salts function eifectively as hardeners only under conditions of low pH and will precipitate out of the stabilizing solution if the pH becomes too high, so that the stabilizing solution must be maintained in a strongly acidic condition. As a result of both the low pH conditions and the presence of high concentrations of thiocyanate ion, the stabilizing bath is highly corrosive in nature and attacks the metal parts of the processing apparatus with which it comes into contact. The corrosion is frequently sufliciently severe that it leads to development of leaks or even complete failure of the apparatus.

It has now been discovered that the corrosiveness of the stabilizing baths described hereinabove can fbe greatly reduced by incorporating therein a minor amount of a polyalkylene glycol. The polyalkylene glycols have been found to function effectively to minimize corrosion problems without exhibiting any deleterious effects on the properties of the bath. Thus, for example, they do not interfere with the ability of the aluminum salt to harden the emulsion layer nor do they retard the rate of drying, and the permanence of the image to light and moisture is not diminished by their presence. The polyalkylene glycols are adequately soluble in the acidic stabilizer solution to permit their incorporation in the amounts required without difficulty and exhibit no tendency to cause foam formation. They also have the additional advantages of low cost and ready availability.

More specifically, the present invention provides an improved aqueous stabilizing composition for use in rapid access processing which comprises a thiocyanate stabilizing agent, an aluminum salt which functions as a hardening agent for photographic emulsion, and a corrosion inhibiting amount of a polyalkylene glycol. Acidic buffering systems which function to control pH and compounds known to the art to function as tonging agents, i.e., agents which stabilize the image against bleaching, are also advantageously included in the improved stabilizing compositions of this invention.

The stabilizing agents of utility for the purposes of this invention are ammonium thiocyanate and alkali metal thiocyanates, such as sodium thiocyanate or potassium thiocyanate, with ammonium thiocyanate being the preferred agent. Either a single thiocyanate compound or mixtures of two or more thiocyanate compounds can be used, as desired.

The useful hardening agents are water-soluble aluminum salts of strong mineral acids such as aluminum sulfate, aluminum nitrate, aluminum chloride, mixed potassium sulfate-aluminum sulfate salts, e.g., common alum of the formula KAI(SO4)2-12H2O, and the like. It is preferred to use aluminum sulfate since it does not increase the corrosivity of the stabilizing bath, rather than a salt such as aluminum chloride which is itself highly corrosive in nature.

The polyalkylene glycols utilized as corrosion inhibitors in 'accordance with this invention are Well known commercially available materials. They consist essentially of recurring alkyleneoxy groups in which the alkylene radical contains 2 to 4 carbon atoms, e.g., ethylene, propylene or butylene. Each alkyleneoxy group may be the same, as in the polyethylene glycols or the polypropylene glycols, or the alkyleneoxy groups may diler as in the mixed polyethylene-polypropylene glycols. Molecular weights can vary from as low as about 200 to as high as about 20,000. Depending on their molecular weight, the polyalkylene glycols range from slightly viscous liquids to waxy solids, "with the lower members of the series being readily soluble in water and the solubility becoming less as the molecular Weight increases. The molecular weight, or whether the compound is solid or liquid, is not critical for the purposes of this invention and any of the known polyalkylene glycols can be incorporated in the stabilizing bath to render it less corrosive.

Preferred polyalkylene glycols for use in the stabilizing baths of this invention are the polyethylene glycols, and especially the polyethylene glycols which have a molecular weight of at least about 500. Polyethylene glycols with a molecular weight below this value can also be used, but they tend to be less effective as corrosion inhibitors. Illustrative examples of commercially available polyethylene glycols which can be used with good results in the stabilizing baths of this invention are those sold by Union Carbide Corporation under the trademarks Carbowax 200, Carbowax 300, Carbowax 400, Carbowax |600, Carbowax 1000, Carbowax 1540, Carbowax 4000 and Carbowax 6000, the numeral serving in each case to indicate the approximate. average molecular weight. Also useful are Carbowax 1500, which is a blend of equal parts of Carbowax 300 and Carbowax 1540 and has a molecular weight of 500 to 600, and a polyethylene glycol which has a mlecular weight of 15,000 to 20,000 and is synthesized by linking Carbowax 6000 molecules with a diepoxide. This material is commercially available under the trade name polyethylene glycol compound 20 M. The methoxy polyethylene glycols, i.e., polyethylene glycols which have a methyl group substituted for the hydrogen atom at one end of the polymer chain, can also be used in the stabilizing baths of this invention and it is intended to include these compounds, as well polyethylene glycol compound 20 M, within the terms polyethylene glycol and polyalkylene glyco as used herein. The methoxy polyethylene glycols are sold under the trademarks Carbowax 350, Carbowax 550 and Carbowax 750.

The stabilizing baths of this invention should be buffered to provide a pH of less than about 4 and preferably less than about 3.5. The buiering system serves to counteract the effect of the alkaline activator bath and acts to maintain the stabilizing bath in a suitable acidic condition which is conducive to good image stability and to retention of the aluminum hardening agent in the solution. Suitable buifers are those which do not complex or precipitate aluminum and which provide adequate buffering capacity. Examples of such buffers are combinations of acetic acid with an acetate salt such as acetic acid-sodium acetate, acetic acid-potassium acetate, acetic acid-ammonium acetate, and the like.

It will ordinarily be desirable to include in the stabilizing bath a toning agent in order to stabilize the image against bleaching. As is known in the art, mercapto azoles, and especially 3mercapto triazoles, are useful for this purpose. Illustrative examples of useful mercapto azoles are 1,2,4-thiazole-3-thiol, S-amino 1,3,4 thiadiazole-Z- thiol, phenyl mercapto tetrazole, and the like.

The proportions of thiocyanate stabilizing agent, aluminum hardening agent, and polyalkylene glycol in the stabilizing bath can be varied over relatively Wide limits in accordance with this invention. The optimum concentration of thiocyanate will depend upon such factors as the nature of the emulsion, the composition of the stabilizing bath, the design of the processor, and the speed at which the element is transported through the processor. Amounts of thiocyanate of from about 5 to about 50 parts per parts by weight of stabilizing bath are ordinarily suitable, with the preferred amount being in the range from about 15 to about 40 parts per 100 parts by Weight. The aluminum salt should be used in an amount suliicient to render the processed element substantially nontacky, such amounts ordinarily being those suicient to provide from about 0.1 to about 2 parts of aluminum per 100 parts by weight of stabilizing bath, and more preferably from about 0.2 to about 1 part of aluminum per 100 parts by weight of stabilizing bath. It is Within the contemplation of this invention to utilize the polyalkylene glycol in any corrosion inhibiting amount. Preferred amounts of polyalkylene glycol are in the range of from about 0.1 to about 10 parts per 100 parts by weight of stabilizing bath, while it is particularly preferred to use an amount in the range of from about 0.5 to about 4 parts per 100 parts by weight. When a mercapto azole is incorporated in the stabilizing bath, it can be used in amounts of from about 0.02 to about 0.5 part per 100 parts by weight of stabilizing bath.

In accordance with conventional practice in rapid access processing, a developing agent which is the same as or diierent than that incorporated in the photographic element can be included in the activating bath. Examples of suitable developing agents include polyhydroxy benzene compounds such as hydroquinone, methyl hydroquinone, chlorohydroquinone, 3,4 dihydroxydiphenyl, catechol, pyrogallol, and the like; aminophenol developing agents such as `N-methyl-p-aminophenol; and pyrazolidone developing agents such as l-phenyl-3-pyrazolidone. The photographic elements treated by the method of this invention can have an opaque support, such as paper or polyoletin-coated paper, or a transparent support such as cellulose acetate, polyethylene terephthalate, polystyrene, polycarbonates, and the like. The emulsion layer can be hardened prior to processing using conventional hardening agents such as formaldehyde.

Rapid access processing with the stabilizing baths of this invention will ordinarily be carried out at room temperature but higher temperatures, up to about F., can be used, if desired. The time for both developing and stabilizing will typically be in the range from a few seconds to a few minutes, depending on the particular processing conditions utilized.

lWhile it is essential to the practice of this invention to incorporate a thiocyanate stabilizing agent, an aluminum hardening agent, and a polyalkylene glycol in the stabilizing bath, as hereinabove described, it may in some instances be desirable to also include other additives known to be benecial components of stabilizing baths. tFor example, it may be desirable to include a sequestering agent for the aluminum salt in order to prevent scum formation. lUseful sequestering agents for this purpose include hydroxycarboxylic acids, aminocarboxylic acids, and the like. Use of tartaric acid as a sequestering agent is preferred. In addition, it will sometimes be desirable to incorporate anti-staining agents and/or anti-foggants in the stabilizing bath, suitable compounds for this purpose being well known.

Preferred stabilizing compositions within the scope of this invention are those comprising, per liter of solution, about to about 350 grams of ammonium thiocyanate, about 50 to about 150 grams of acetic acid, about 10 to about 50 grams of sodium acetate, about 20 to about 40 grams of aluminum sulfate, about l to about 5 grams of tartaric acid, about 0.2 to about 2 grams of 1,2,4- triazole-S-thiol, and about 5 to about 30 grams of a polyethylene glycol having a molecular weight of at least about 500. (In each instance the balance of the solution consisting of water.) -Especially good results with respect to image stability, handling characteristics of the processed element, and freedom from corrosion of the processor, are provided by a stabilizing composition comprising, per liter of solution, about 300 grams of ammonium thiocyanate, about 75 grams of acetic acid, about 30 grams of sodium acetate, about 30 grams of aluminum sulfate, about 2 grams of tartaric acid, about 1 gram of 1,2,4-trazole-3-thiol, and about 20 grams of a polyethylene glycol having a molecular weight of at least about 500.

The improved stabilizing baths of this invention can be used wherever thiocyanate stabilizing baths have heretofore been employed and will provide at least as good results as regards the quality of the processed element while, as a result of the presence of the polyalkylene glycol, they will exhibit a substantially reduced tendency to corrode processing equipment. They may be used with any of the known types of processors, employing conventional processing conditions with respect to such factors as temperature and rate of throughput. They are especially useful with high speed incorporated-developer papers utilized in wirephoto operations.

The invention is further illustrated by the following examples.

Photographic elements were processed in a conventional rapid access stabilization processor employing an activating bath consisting of a solution of sodium sultite, sodium hydroxide, and potassium bromide in water. In a rst series of tests, the aqueous stabilizing bath was of the following composition:

'Concentration Component: (grams per liter) Ammonium thiocyanate (NH4SCN) 300 -Glacial acetic acid 76 Sodium acetate 30 Aluminum sulfate (A12(SO4)3) 29 .Tartaric acid 2.5

1,2,4-triazole-3-thiol 1 In a second test series, the aqueous stabilizing bath was of the same composition as that described above except that it also contained 20 grams per liter of polyethylene glycol sold under the trademark Carbowax 1540. In each instance the pH of the bath was 3.2. In both test series the prints obtained were essentially equivalent with respect to image stability and handling properties and were fully satisfactory for commercial use of the process. The stabilizing bath containing the polyethylene glycol was found to be substantially less corrosive to the processor. Similar results are obtained when other polyalkylene glycols, as hereinbefore described, are substituted for the Carbowax y1540.

EXAMPLE 2 To demonstrate the reduced corrosion resulting from use of polyalkylene glycols in accordance with the teachings presented herein, a series of corrosion tests were conducted. These tests were carried out at a temperature of 100 F. using passivated AISI-34 stainless steel billets with dimensions of 2 inches x 1 inch x 1/32 inch and a weight of 9 grams and with the billet half immersed in the solution. The stabilizer solutions tested had the same composition as described in Example 1 except that they contained varying amounts of different polyalkylene glycols as the corrosion inhibitor. 'Ihe polyalkylene glycols used were polyethylene glycols sold under the trademark Carbowax, as hereinbefore described. In carrying out these tests, the billet was removed from the solution after a period of 7 days, cleaned, and weighed. If there was found to be a loss in weight due to corrosion of less than one percent, then the solution was replaced with fresh solution of identical composition and the test was continued (the purpose of such replacement being to eliminate any variation in result due to degradation of the solution).

The test conditions and results obtained are summarized in the following table.

Concentration of polyalkylene glycol (g./1. Weight loss of stabiliz- Duration (percent o ing soluof test initial Polyalkylenc glycol tion) (days) Weight) None 7 5. 84 Carbowax 200 22 7 3. 66 Carbowax 300- 22 7 3. 59 Crbowax 350. 22 24 0. 66 Carbowax 400 22 7 2. O3 Carbowax 550 20 52 0. 15 CarboWax 600 20 38 l). 44 Carbowax 750 20 52 0. 12 Carbowax 1000. 20 tu 0. 14 Carbowax 1500 20 52 0. lll Carbowax 1510- 2 126 0. 68 20 161 0. 14 2 28 l. 4l 20 70 0. 08

As indicated by the tabulated data, the incorporation of a polyalkylene glycol in the stabilizing bath substantially reduces the corrosion of stainless steel in contact with the bath. For example, the data shows that without any polyalkylene glycol a weight loss of 5.84 percent occurred in 7 days, whereas incorporation of 20 grams of Carbowax 1540 per liter of solution resulted in a weight loss of lonly 0.14 percent in 161 days. As will be apparent, this is an important advantage in reducing operating problems and prolonging the life of processing equipment which substantially enhances the commercial usefulness of rapid access processing.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. An acidic aqueous composition for stabilizing developed silver photographic images comprising a thiocyanate stabilizing agent, an aluminum salt which functions as a hardening agent for photographic emulsion, and a corrosion inhibiting amount of a polyalkylene glycol said polyalkylene glycol contains 2-4C alkylene groups and has a molecular weight of about 200 to about 200,000.

2. The composition described in claim 1 wherein said thiocyanate stabilizing agent is present in a proportion of from about 5 to about 50 parts per 100 parts by weight of said composition, said aluminum salt is present in a proportion providing from about 0.1 to about 2 parts of aluminum per parts by weight of said composition, said polyalkylene glycol is present in a proportion of from about 0.1 to about 10 parts per 100 parts by Weight of said composition, and wherein said composition is buffered to a pH of less than about 4.

3. The composition descrbed in claim 1 wherein said thiocyanate stabilizing agent is present in a proportion of from about l5 to about 40 parts per 100 parts by weight of said composition, said aluminum salt is present in a proportion providing from about 0.2 to about 1 part of aluminum per 100 parts by weight of said composition, said polyalkylene glycol is present in a proportion of from about 0.5 to about 4 parts per 100 parts by weight of said composition, and wherein said composition is buffered to a pH of less than about 3.5.

4. The composition described in claim 3 additionally comprising a minor amount of a mercapto azole.

5. The composition described in claim 3 additionally comprising a minor amount of tartaric acid.

6. The composition described in claim 3 wherein the thiocyanate stabilizing agent is ammonium thiocyanate.

7. The composition described in claim 3 wherein the aluminum salt is aluminum sulfate.

8. The composition described in claim 3 wherein the polyalkylene glycol is a polyethylene glycol with a molecular Weight of at least about 500.

9. The. composition described in claim 3 wherein buffering is effected by a combination of acetic acid and sodium acetate.

1t). An acidic aqueous composition for stabilizing developed silver photographic images comprising, per liter of solution, about 150 to about 350 grams of ammonium thiocyanate, about S to about 150 grams of acetic acid, about 10 to about 50 grams of sodium acetate, about 20 to about 40 grams of aluminum sulfate, about 1 to about grams of tartaric acid, about 0.2 to about 2 grams of 1,2,4-triazo1e-3-thiol, and about 5 to about 30 grams of polyethylene glycol having 2-4C alkylene groups and at molecular weight of at least about 500.

11. An acidic aqueous composition for stabilizing developed silver photographic images comprising, per liter of solution, about 300 grams of ammonium thiocyanate, about 75 grams of acetic acid, about 30 grams of sodium acetate, about 30 grains of aluminum sulfate, about 2 grams of tartaric acid, about 1 gram of l,2,4triazole-3 thiol, and about 20 grams of polyethylene glycol having 2-4C alkylene groups and a molecular weight of at least about 500.

12. In the method of stabilization processing of imagewise exposed silver-containing photographic elements cornprising contacting the exposed element with an activating solution to develop it and then contacting the developed element with an acidic stabilizing composition comprising a thiocyanate stabilizing agent and an aluminum salt which functions as a hardening agent for photographic emulsion, the improvement comprising incorporating in said stabilizing composition a corrosion inhibiting amount of a polyalkylene glycol said polyalkylene glycol contains 2-4C alkylene groups and has a molecular Weight of about 200 to about 200,000.

13. The method of claim 12 wherein the polyalkylene glycol is incorporated in the stabilizing composition in an amount of from about 0.1 to about 10 parts per 100 parts by weight.

14. The method of claim 12 wherein the polyalkylene glycol is incorporated in the stabilizing composition in an amount of from about 0.5 to about 4 parts per 100 parts by weight.

15. The method of claim 14 wherein said polyalkylene glycol is a polyethylene glycol having a molecular weight of at least about 500.

References Cited UNITED STATES PATENTS 2,378,247 6/1945 Russell 96-61 2,614,927 11)/1952 Broughton 96-61 2,759,823 8 1956 Kridel 96-61 FOREIGN PATENTS 1,187,170 9/1959 France 96-61 OTHER REFERENCES British Journal of Photography, Chemistry of Stab. Processing, Nov. 24, 1967, pp. 1009-1012.

NORMAN G. TORCHIN, Primary Examiner M. F. KELLEY, Assistant Examiner U.S. Cl. XR. 96-95 

